Update: Anadarko details find off Sierra Leone

The 45 ft of net hydrocarbon pay cut by an Anadarko Petroleum Corp.-operated deepwater exploratory well off remote Sierra Leone was only part of a “tremendous amount” of reservoir-quality rock the well penetrated, company officials said.

Sep 16th, 2009

This story has been updated from an earlier posting.

Alan Petzet
OGJ Chief Editor-Exploration

HOUSTON, Sept. 16 -- The 45 ft of net hydrocarbon pay cut by an Anadarko Petroleum Corp.-operated deepwater exploratory well off remote Sierra Leone was only part of a “tremendous amount” of reservoir-quality rock the well penetrated, company officials said.

Anadarko and partners were still logging the well Sept. 16, had not yet seen analyses of hydrocarbons recovered to surface by a modular formation dynamics test (MDT) tool, and were still receiving 3D seismic shot off Liberia to the east. The discovery is a technical success and could be highly commercial, they said.

Anchoring a conference call were Anadarko’s Al Walker, chief operating officer; Bob Daniels, senior vice-president, worldwide exploration; and Frank Patterson, vice-president, exploration.

All information from the well “is very positive for the exploration effort in the Liberian and Ivorian basins,” including fan systems, petroleum system, thermal maturity, and migration, said Daniels. The well proved the fan systems get better coming off the craton.

In the Venus well Anadarko saw good reservoir quality in numerous sands and shows in numerous sands. Nine wells previously were drilled on the shelf off Sierra Leone, and Venus validated the geological parameters of the depositional model that are going to help the company and its partners set up the rest of the play, they said.

After the group drilled to the originally prognosed 5,000 m, the well was still in fans and seeing hydrocarbon shows and elected to continue to the final TD of 18,500 ft.

The well found a combination stacked channel and fan complex, and both facies can be productive, Anadarko said.

One source rock encountered in the Venus well is immediately adjacent to reservoirs, and the area could contain other source rocks not yet penetrated, the company said.

A lot of data are still to be collected to determine where to drill the next well at Venus, but a dip rate of 2-7° indicates that areal extent of the reservoirs could be quite large. Areal extent, still to be determined, will become clearer after well and log data are tied with existing 3D seismic data.

Anadarko didn’t reveal the geothermal gradient but said it shows that the kitchen is kicking out large amounts of hydrocarbons.

The drillsite is not at each zone’s optimal location on the prospect. Rather, the well is in the best position to obtain as much data as possible on the multiple targets in the stratigraphic section to be penetrated, Anadarko said.

Anadarko’s goal is to drill opportunities to discover more than 150 million to more than 1 billion gross barrels of oil equivalent, and it sees multiple such features on all of the 10 blocks in which it participates off Sierra Leone, Liberia, Ivory Coast, and Ghana.

Anadarko was able to obtain a majority of the best acreage off the four countries and had done enough preparatory work to know what acreage to pursue and which to avoid. Even so, it might show interest in a few more blocks, and Venus has substantially derisked the acreage, the company said.

After completing work at Venus, the rig will drill the South Grand Lahou prospect off Ivory Coast in the western part of the Ivorian basin. The South Grand Lahou fan system looks like giant Jubilee oil and gas field off Ghana did before it was drilled, Anadarko said.

The rig will then move to drill the Windjammer prospect off Mozambique (OGJ Online, June 25, 2009).

Anadarko plans to drill two to five wells in 2010 in the Cretaceous Trend. Venus B-1, the first deepwater test in the Sierra Leone-Liberian basin, went to 18,500 ft in 5,900 ft of water on Block SL 6/07 about 55 miles from Liberian waters.

Venus is one of more than 30 prospects and leads Anadarko has identified on its West Africa acreage position. That includes interests in nearly 8 million acres on 10 blocks off Sierra Leone, Liberia, Ivory Coast, and Ghana. Anadarko operates seven of the blocks and the majority of the prospects with 40% average working interest.

“With Jubilee (off Ghana) on the east and Venus on the west, we have established bookends spanning approximately 1,100 km (700 miles) across two of the most exciting and highly prospective basins in the world,” said Daniels.

Sierra Leone has no oil or gas production. Venus is near the northwestern end of a 3,700 sq km 3D seismic survey on blocks SL 6/07 and SL-7 off Sierra Leone. That survey adjoins a 6,000 sq km 3D seismic survey on Blocks LB-15, LB-16, and LB-17 off Liberia. Seismic shooting is under way on Block LB-10 off Liberia.

Venus is also 850 miles south of oil and gas discoveries in the Atlantic off Nouakchott, Mauritania (see map, OGJ, Oct. 23, 2006, p. 38).

Interests in Venus are Anadarko 40%, Woodside Energy Ltd. and Repsol YPF SA 25% each, and Tullow Oil PLC 10%.

Contact Alan Petzet at alanp@ogjonline.com.

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